Airbags for motor vehicles are known and have been used for a substantial period of time. These devices are installed on the driver and passenger side of automobiles and, in the event of a collision, are rapidly inflated with gas, to act as an energy absorbing barrier between the driver or passenger and the steering wheel or dashboard of the automobile.
More recently, airbag safety restraints in the form of an inflatable restraining curtain disposed along the side of a vehicle between an occupant and window or door openings have played a well recognized role in preventing injury to the occupant during a collision event. Typically, such curtains are inflated rapidly by the pressure of a reaction gas released from an inflator at the outset of the collision event. This gas generation usually takes place when a gas-generating agent in the inflator induces a chemical reaction activated by a collision signal from a collision detecting sensor when deceleration of the vehicle exceeds a certain level. The gas which is generated by the inflator is then conveyed to the airbag curtain. Inflatable curtains are typically deployed downwardly from a storage position along the roof rail so as to at least partially cover window and/or door openings across the side of the vehicle. The deployed curtain thus provides both a degree of cushioning restraint as well as a barrier preventing the occupant from being ejected from the vehicle. Due to the extended duration of a roll-over collision event where the vehicle may turn over several times it is desirable for the curtain-type airbags to remain inflated for an extended period of time so as to maintain a degree of head protection and barrier restraint until the entire event is concluded.
Curtain-type airbags are typically formed by sewing together panels of fabric to form a plurality of pillows when inflated or by weaving two layers of fabric that are interconnected at certain areas in a Jacquard loom. Such pillowed fabrics typically utilize seams which control the shape and size of the inflated cushion. Upon inflation of these airbag cushions in response to a collision event, pressure is applied in great force, particularly on the seams and can result in seam combing. In this regard it is to be understood that the term “seam combing” refers to the phenomenon wherein applied pressure causes the seaming threads to spread apart and thereby release additional gas pressure.
Performance can be improved by applying substantial quantities of permeability blocking coating materials. In the past, coatings have been applied to fabrics intended for use in automotive airbags in order to resist the unwanted permeation of gas through the fabric and, to a lesser extent, to protect the fabric from detriment by the hot gases used to inflate the bags. Polychloroprene was utilized in the early development of airbags. More recently, silicone (polydimethylsiloxane or similar materials) has gained increasing acceptance.
Since the airbag must retain its integrity during a collision event, in order to sufficiently protect the driver or passenger, there is a great need to provide coatings which provide both effective permeability characteristics and sufficient restriction of seam combing for the airbag to function optimally, if and when necessary. Thus, there exists a need for providing good adhesion and a strong bond between the individual yarns in order to effectuate long-term rigidity of the fibers to prevent unraveling at cut edges or at seams while simultaneously providing aging stability and excellent low air permeability characteristics.
One approach to decreasing coating weights while maintaining low permeability performance of the airbag fabrics has been to use a two layered coating system, as disclosed for example in commonly assigned U.S. Pat. Nos. 6,177,365 and 6,177,366 to Li (all hereby incorporated by reference in their entirety). Alternative coating compositions have been disclosed based on polyurethanes, such as in U.S. Pat. No. 5,110,666 or on polyurethane/polyacrylate dispersions as found in commonly assigned U.S. Pat. No. 6,169,043 (all hereby incorporated by reference in their entirety).
Current industry practice typically utilizes conventional coating methods employing solvent or water based coatings for airbag fabrics. Consequently, the solvent or the water needs to be removed by drying and the organic polymer needs to be cured by subsequent exposure to heat. The coating method is predominantly some form of knife over air/gap or transfer coating.
An alternative approach is to laminate polymeric films to the airbag fabric. Traditional lamination methodology employs a tie coat of an adhesive layer on the fabric before film lamination. This type of approach is taught in U.S. Pat. No. 6,770,578, U.S. Pat. No. 6,908,528, and U.S. Pat. No. 6,753,275 (all incorporated by reference in their entirety), all of which teach application of an adhesive layer as an aqueous or solvent containing dispersion which necessitates the removal of water or solvent at a subsequent point in the process.